Traveling wave tube



sept. 16, 1952 P, G, BOHLKE 2,611,102

TRAVELING WAVE TUBE Filed NOV. 13, 1948 INVENTOR. P aut 6'. O/Il/e Patented Sept. 161,

`Paul GIBohlke; lFlushing, N.Y.,"assigno'r to Sy'l-Iv vania-E1ectric'Products Inc., a corporation of Massachusetts..

Application November 13, 1948,.Seral.No. v593577,85

[The present invention yrelates 'totravelingV wave tubes, a type of electronic amplifier. This type of tube ordinarily .includes an electron gun at one extremity, an electron .collector at vthe opposite extremity,.signal input .and loutput coupling devices or probes neareachextremity,,and a hollow transmission line. betweenthe probes. The transmission line .isi toreshcrtened, to be of greater effective lengthY 'than .the physical. distance between the input and output probes,.and is commonly in the form of a helix .or it mayinclude two or more helices. Anenvelope otgla'ss or equivalent material encloses .the several .ele. ments described. Low-loss'rods of ceramic, quartz or like material space the hollow .transmission line inward of the` glass envelope .to .fix the .position and maintainalignment ofthe transmission line, and to avoid .thermal damage to the .glass envelope due to heating. of the hel-mand to avoid attentuation in the usually soft tand relatively7 lossy glass wall. An .electron beam is .directed longitudinally within the transmission line, and interacts with the fields alongthe line `to yield amplified signal energy.

Wave guides are ordinarily vusedior `couplingsignals into and out of.the..traveling-Wave tube, these wave guides being penetratedbythe trav-l eling-wave tube. The Wave .guides .surroundthe tube in the regions of the inputfandoutputlcou.- pling devices. A choke is r.includezlnear each probe for impedance matching, and .toprevent stray coupling and loss of energy towardthe-ends of the traveling-wave tube. Because the tube envelope constitutes a sleeve -of insulatingmaterial, the chokes used .heretofore'necessarily,have been of the open-termination .nominally halfwave variety. The traveling-wave -tube y is :intrinsically a long andslender structure,and this length is extended by the half-Wave chokes required.

With respect to this prior-art construction, there is the possibility ofcircumferential moding about the holes in the V-wave guides ythat receive the traveling-wave tube. This possibility can-be reduced, and higher operatingl:frequencies attained, by decreasing the outer diameter .ofthe tube envelope so as to decrease the required size of. the hole in the Wave guide.r This expedient, of course, has its limitations.

Traveling-wave tubes of the vforegoingvariety are improved in severalA .respects in accordance with this invention through the use of discs-or rings sealed through'the 'envelope wall.- The inner edgesof such rings are formedtto receive the low-loss rods or like insulating supportthat `carries the transmission line, thereby making-unnecessary the otherwise closetoleranoe requiredof the straightness and of the inner diameter Vofthe glass tubing used in forming the envelopeof the conventional tube.. Such ,ring,.f-,or vdlscas .it .is

'v i claims. (01; eis-esi' e alternatively termed; can. be used to advantage at any point 'along `the tube Wheremechanical support lisr'iesired.V I-I'owever,ift-iseofr special value in lthe vreg-'ions 'of the .input andoutpuit coupling devices where pairs Vof discjterminals canj be spaced apart a vdistance equal --to Ya transversedimension of .the inputfand 'output lwave guides', thereby extending the wave-guide wallsy into intimate relation withv 4the probes. The holes through the several discsv are no longer required to be large enough to admit the tube envelope, butcan .be 'made Yconsiderably smaller, and accordingly the possibility `of circumferential moding isV reduced. The disc terminal which penetrates the tube envelope enables tueuse of shorted nominally quarter-wave matching stubs `within the tube envelope inlplace of thelongergopen half-wave Astubs used withjtubes 'of the prior-.art construction. n

'The novel features of theinventionare dened in the appended claims, andwillbe better ap' preciated from the followingY detailed disclosure of two illustrative embodiments in the accom' panyng drawings, in which :A

Fig; 1 is a longitudinal cross-section of atraveling-jwave tube embodying novel .features ,of the invention, additionally including input and .output wave guides;

Fig. l2 Vis a transverse sectionalview along .the line ZLZ of Fig. 1,;

Fig. 3 'is a fragmentary ,vie'w of, a 'traveling-- wave 'tube like that otFig. ,1 Iin all respects except for the modified details illustrated; and.,

Fig. 4 is a transverse sectional View along the` line 4 4 of Fig. 3.

Referring now rto Fig. 1 .a traveling-wave tube is vshown having anenclosing .envelope .l 0- vconveniently of softglass.. an electron gun liiatv one extremity, and .collector electrode '1i at the .coposite extremity, this tubebeing about thirty times as long as its diameter. An inputccupling. device or probe 1'6 near gun ,L2 andan output coupling device or probe .i8 'near collector ,Ill are of hollow form and provide. a pathior .the electronbeam that is to travel .lengthwise .ofthe tube. Atransmission line 1'2'0 Lis supportedbetween probes .I6 and ,18 by three longitudinally disposed .lowfloss rods 22l '(see Fig.. 2).,xadvantageously.ofhard gloss. This 'transmission line, physically foreshcrtened in relationto `its electricallength, here .takesthe form of Vahelical conductonand is of .suohpro-l portions thatthe signal .induced .at the inputend will travel along the conductor at. aspeed which has a retarded component along the .travelingwave .tube .commensurate with thespeedoi vthe electrons .inthe beam. Low-loss rods permitv the use of akind ofglass throughoutjtheitube.

which is of `such nature ,that sealsl -foremerg-i-ng electrode .leads can 'be readily formed, .mag-1 netic coil.V .(no't shown) .ordinarily enciroles-the other. An input wave guide 24 operating in the TEoi mode is associated with probe I6 with the electric field along the probe, and an output wave guide 26 is similarly associated with output probe The mechanics of amplification in the traveling-wave tube are understood generally, and are the same for the prior-art construction as in the present improved form of traveling-wave tube. Oscillatory energy is coupled from rectangular input wave guide 24 to probe I6 and input end of helix 20. Because of interaction between the induced wave which then travels along the helical wire at roughly the speed of light and the electron beam which travels a straight line path along the tube axis and the axis oi the helix at a much lower speed, the electrons in the electron beam become bunched, and energy of the bunched electron beam is in turn abstracted by succeeding portions of the helix which also accentuate the bunching of the electrons. The oscillatory energy which appears at the output end of helix 2t and output probe I8 is much greater than that at the input end, and is coupled into output wave guide 26. Lumped attenuators (not shown) are provided at one or more points along the helix to suppress reected waves.

Discs 28, 30, 32 and 34 are sealed through the wall of envelope I in alignment with the respective walls of wave guides 24 and 26. Discs 38 and 32 are circularly apertured to provide a passage for helix 28, and the circular aperture of each disc is notched at three points to receive three rods 22 snugly. Rods 22 are accurately positioned by means of the simple and easily formed metal discs 38 and 32 that are sealed through the tube wall, with their apertures centered about the tube axis and their rod-receiving recesses in alignment. Better accuracy at lower cost can be realized with this arrangement than in the prior-art construction where the inside wall of the glass tubing forming the envelope, closely controlled for diameter and straightness, is relied on to conine the low-loss rods against the helix.

A portion of each disc 23, 38, 32 and 35 outside envelope I8 is spun over a stiffening ring 36, the discs here being formed of thin sheet-copper. In some instances, it is desirable to provide a disc centrally apertured as in Fig. 2 for mechanical support of the helix or like element at a point between the input and the output wave guides, and Where no external electrical contact is required. The external portion of the disc and its*l ring 36 may be omitted in such case.

Discs 28 and 34 are formed alike, and, in the form of traveling-wave tube shown in Fig. 1 these discs act as mechanical supports and electrical contacts for the input and output coupling devices I 6 and I8 respectively. They also enable the use of nominally quarter-wave chokes or matching stubs comparable to the open half wave lines outside the tube envelope used with prior art traveling-wave tubes.

Probe or coupling device I6 is supported centrally within rods 22, and this probe is extended axially toward the electron gun. It constitutes the inner conductor of coaxial choke 38, the outer conductor 40 of which is joined to the probe by shorting ring 42. The opposite open end of outer conductor 4D is fitted snugly into a cylin- 4 drical portion formed integrally with the internal part of disc terminal 28, a shoulder 42 being formed externally on outer conductor 40 to limit its displacement down the traveling-wave tube to the position shown. Sealed-in disc 28 thus acts as a continuation of one wall of wave guide 24, and, with shorted stub 38, provides a matching `impedance between the wave-guide and the probe, and effectively closes off any leakage of oscillatory energy toward the gun end of the tube.

Sealed-in disc 34 is formed similarly and supports another snorted quarter-wave stub 44 as well as output probe I8. Helix 20 is joined to probes I6 and I8, being tensioned between them and thus urges the externally shouldered quarter- Wave coaxial lines endwise against the respective discs 28 and 34. The diameter of the central apertures in discs 28 and 34 is so small that a relatively high operating frequency would have to be reached before raising the possibility of circumferential moding, as true also of discs 30 and 32. This contrasts with the inherently larger holes in the wave-guides penetrated by the glass envelope of the prior art traveling-wave tube described. Discs 28 and 34 also limit the endwise displacement of rods 22. It will thus be apparent that sealed-in discs 28, 38, 32 and 34 support the input and output probes and, via rods 22, support the helix 28 as well. There is an evident advantage in substituting the accurately controllable metal discs as the spaced point-supports for the high-frequency electrodes rather than to rely on the straightness and accurate diameter of the inner bore of the glass tubing. In forming the seals, precaution must naturally be taken to assure axial alignment of the several discs, advantageously utilizing internal jigging and sealing procedures as in copending application, Serial No. 612,029, filed August 22, 1945, by Paul Haas.

Figs. 3 and 4 illustrate a modification of the traveling-wave tube shown in Fig. 1. Where applicable, primed numerals are used to designate parts corresponding to those of Fig. l. Only 1 input probe I6' and terminals 28 and 3G for coupling to the input wave guide are shown, the output components being reversely symmetrical. Metal tube 46 is enclosed within envelope I8' to form a shield about helix 28', such shield sometimes being considered necessary. Low-loss rods 22', preferably of a ceramic material in this instance, are confined against helix 28 to support it within shield 46, the shield being in turn supported at each end by one of the sealed-in discs, as 38. Rods 22' extend into shorted matching stubs 38 and are constrained against endwise displacement by eyelets at each end of each rod, only one 48 of which is shown in Fig. 3 gripping a rod 22'. As shown in Fig. 4, four rods 22 are used in this instance. Spacing is allowed to accommodate differences in thermal expansion of the several parts.

Rods 22' support the input and output probes and the connecting helix 28 and are in turn supported not by the inside surface of the glass tubing, but by discs sealed through the wall of the tube envelope. The discs constitute mechanical support; they extend the 'wave-guide walls thereby reducing the diameter of the necessary apertures; and the sealed-in discs enable use of short-circuited coaxial stubs of comparatively short axial dimension in substitution for the prior-art open half-wave stubs.

While the invention is shown as having particular application to the form of travelingwave tube employing a helical wire as the foreshortened transmission line for the traveling wave, several of the features of the invention will be found to have application to other forms of traveling-wave tubes. This, and other applications of the invention and varied detailed modiflcations will occur to those skilled in the art. Therefore, the appended claims should be allowed such broad interpretation as is consistent with the spirit and scope of the invention.

What is claimed is:

1. A traveling-wave tube comprising a generally tubular long and slender glass envelope, an electron gun at one extremity, an electron collector at the opposite extremity, a tubular input probe near said electron gun, a tubular output probe near said collector, a helical-wire transmission line between said probes, said probes and said transmission line providing a path for an electron beam from said gun to said collector, a plurality of low-loss rods in external engagement at spaced peripheral points with said probes and with said transmission line, a pair of discs sealed through said glass envelope and in contact with said rods near the extremities of said transmission line, said rings having formed portions receiving said rods and preventing peripheral displacement of the rods circumferentially about the helical-wire transmission line, short-Circuited coaxial lines joined each to one of said probes and utilizing as its central conductor an extension of a respective probe, said short-circuited lines extending oppositely from said probes toward the extremities of the envelope, an additional pair of metal discs sealed through the glass envelope at the input ends of said shorted lines and in supporting relation thereto, the two metal discs associated with each of the respective probes being spaced apart to act as continuations of input and output wave guides.

2. An electron discharge device comprising an envelope, an electron gun for producing a beam of electrons, a pair of disc terminals sealed through the envelope transversely and apertured centrally, thus allowing penetration by the electrons, said discs providing externally available terminals, and a coaxial line within said tube short-circuited at one end and having the outer conductor of the opposite open end secured to one of said discs, the center conductor of said coaxial line being tubular and providing a patch for the electrons.

3. A traveling-wave tube comprising a glass envelope, means to project an electron beam longitudinally of said envelope, a pair of disc terminals sealed through said envelope and having externally available portions for connection to a wave guide, a probe within the tube between said discs, and a short-circuited coaxial line joined to said probe and to one of said discs at the open end of the line, the center conductor of said line being tubular to provide a path for the electron beam.

4. A traveling-wave tube comprising a long and slender generally tubular glass envelope having a pair of metal discs sealed through the envelope wall at an input end, an electron gun at said input end, an electron collector at the opposite end of said envelope, another pair of metal discs sealed through said envelope wall adjacent said collector, a pair of short-circuited quarterwave coaxial chokes each carried by a respective one of the discs closest to said electron gun and said collector, the center conductor of said coaxial chokes being tubular and providing a path for an electron beam between said gun and said collector, and probes extending into the space between the input and the output pair of discs, said probes being electrically and mechanically connected to said center conductors.

5. A traveling-wave tube comprising a long and slender generally tubular glass envelope having an electron gun at one end and an electron collector at the opposite end, an input pair of disc terminals sealed through said envelope adjacent the electron gun, an output pair of disc terminals sealed through the envelope adjacent the collector end of said envelope, a pair of short-circuited coaxial lines each having its open end connected to a respective one of the disc terminals closest to said electron gun and to said collector, the center conductor of each coaxial line having a tubular extension into the regions between the input discs and the output discs, a helical-wire transmission line joined to the tubular extensions, and supporting means for said probes and said transmission line supported by those disc terminals opposite the quarterwave lines. said supporting means including plural low-loss rods in lateral engagement with said probes and said helical-wire transmission line.

6. A traveling-wave tube comprising a generally tubular glass envelope, means for projecting an electron beam axially within said tube, wave transmission means including a helical conductor substantially coaxial with lsaid tube, plural metal rings sealed through said envelope at axially spaced points, and low-loss insulating means confined radially between said rings and said helical conductor, said insulating means extending along the helical conductor and providing an aligning support therefor.

7. A traveling-wire tube comprising a tubular envelope, means for projecting an electron beam axially within said envelope, a helical wire within said envelope, plural substantially straight low-loss insulating rods about said helical wire, and plural discs spaced apart and sealed transversely through said envelope, said discs being in engagement with said rods and confining the helical wire substantially coaxially within the envelope, said discs having axially aligned notches confining the rods against peripheral displacement.

PAUL G. BOHLKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,064,469 Haeff Dec. 15, 1936 2,153,728 Southworth Apr. 11, 1939 2,367,295 Llewellyn Jan. 15, 1945 2,400,753 Haei May 21, 1946 2,450,026 Tomlin Sept. 28, 1948 2,488,906 Gardner Nov. 22,1949 2,521,760 Starr Sept. 12, 1950 OTHER REFERENCES Article by Kompfer, pp. 124-127, Proc. of I. R. E. and Waves and Electrons, vol. 35, No. 2, February 1947.

Article by J. R. Pierce, pp. 439-442, Bell Lab. Record, December 1946. 

